The standard syntax includes constructs introduced by the # character.
The syntax of these constructs is as follows:
a character that identifies the type of construct is
followed by arguments in some form.
If the character is a letter, its case is not important;
#O and #o are considered to be equivalent, for example.

Certain # constructs allow an unsigned decimal number to appear
between the # and the character.

Note also that digits do not appear in the preceding table. This is
because the notations #0, #1, ..., #9 are
reserved for another purpose which occupies the same syntactic space.
When a digit follows a sharpsign,
it is not treated as a dispatch character.
Instead, an unsigned integer argument is accumulated
and passed as an argument to the reader macro
for the character that follows the digits.
For example,
#2A((1 2) (3 4)) is a use of #A with an argument of 2.